Piston



FIG. 1 is a side elevational view of a piston, showing my new design theother side being identical thereto;

FIG. 2 is a front elevational view thereof, the rear being identicalthereto;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a sectional view taken along the line V--V of FIG. 1,

FIG. 6 is a sectional view taken along the line VI--VI of FIG. 2; and

FIG. 7 is a top side perspective view thereof.

The ornamental design for a piston, as shown and described.